Based on methods of isolation of purified mammalian parietal cells it is proposed to further separate the membranes of these cells into apical and basal lateral fractions and further characterize these by (1) morphologic and compositional studies, (2) hormonal effects on basal and apical surfaces, (3) purification of 2 major peptides assumed to be of apical origin, (4) studies on the H ion, cation and anion transport properties of the isolated membrane vesicles.